Radio aid to navigation



G. C. LUCK RADIO AID TO NAVIGATION Filed Dec. 24, 1946 2 Sheets-Sheet 1l L SINGLE MOD. 8/05 541w MOD. l l r MOD L H f F 05c. 05c. IKC. aon/ 37[37 F/LTER REC! L (B45353 ULATOR um) 4 PHASE 47 L 1 MTER PHASE F/LTEI?0:72am? Assj-s ADJ 47 1 51 PHASE SH/FTEI? I Inventor DavJJ G. OLuck(Ittorncg Jan. 2, 1951 N D. e. c. LUCK 2,536,509

RADIO AID TO NAVIGATION Filed Dec. 24, 1946 2 Sheets-Sheet 2 LOWER UPPER5/05 BAA/D FREQ M00 5/05 BAND M00. M00. M00.

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3nventor DavfdGZ Cluck Gttorneg Patented Jan. 2, 1951 UNITED STATESPATENT OFFICE RADIO AID T NAVIGATION David G. C. Luck, Princeton, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication December 24,1946, Serial No. 718,219

6 Claims.

This invention relates to radio aids to navigation, and moreparticularly to improvements in to provide an omnidirectional radiorange system 'aflording a higher degree of sensitivity or sharpness ofbearing indication than has been achieved heretofore by omnidirectionalranges.

Another object of the invention is to provide a system of the describedtype which is readily adapted for direct visual indications of bearing,using substantially the same equipment ordinarily employed withconventional omnidirectional radio ranges.

The invention will be described with reference to the accompanyingdrawing, wherein:

Figure 1 is a schematic block diagram of a range transmitter systemembodying the invention; Figures 2, 3, 4 and 5 are polar graphs showingtypical radiation patterns produced in the operation of the system ofFig. 1; Figure 6 is a schematic block diagram of a typicalomnidirectional radio range receiver which may be used in conjunctionwith the system of Fig. 1; and Figure '7 is a schematic diagram of amodification of the system of Fig. 1.

Refer to Figure 1. Two antennas I and 3, each by itself having asubstantially circular directive pattern in the horizontal plane, arespaced horizontally apart by a distance nl, substantially greater thanone wavelength A at the frequency at which the range is to operate. Theantennas I and 3 may be in the form of vertical towers, as high as isstructurally and economically feasible, and a ty ical spacing betweenthem may be two wavelengths. For long-range operation, a low carrierfrequency. of the order of 100 kilocycles per second, is preferred.

A radio frequency oscillator 5 is coupled to the antenna I through amodulator I, and to the antenna 3 through a single sideband modulator 9;The single sideband modulator 9 may comprise a balanced modulator andsideband filter, or anyother known apparatus providing suppression ofthe carrier and one sideband of a modulated radio frequency signal.

The modulation input terminals of the modulator 9 are connected to anoscillator I! which provides an output of alow audio frequency, forexample 30 cycles per second. The oscillator II is also coupled to themodulation input termina of a third modulator I3. An oscillator I5,operating at an intermediate audio frequency such as 1000 cycles persecond, is coupled through the modulator I3 to the modulation inputterminals of the modulator I.

In the operation of the system of Figure 1, the antenna I radiates asignal comprising a kilocycle carrier modulated by a 1000 cyclesubcarrier which is in turn modulated at 30 cycles per second. Bothsidebands of the 100 kilocycle carrier are present, each includingcomponents differing from the carrier frequency by 1000 cycles persecond, 1030 cycles per second, and 970 cycles per second.

The antenna 3 radiates only one sideband of the 100 kilocycle carriermodulated at 30 cycles per second. Assuming the lower sideband to besuppressed with the carrier in the modulator 9, the antenna 3 radiates asignal comprising a single component whose frequency is 100,030

cycles per second. This may be regarded as, and in fact is, the samething as a 100 kilocycle signal which is being advanced in phasecontinuously at the rate of 10,800 per second or 360' degrees per cycleof the low frequency oscillator II.

The 100 kilocycle carrier signal radiated from the antenna I combineswith the signal radiated from the antenna 3 to provide a space patternwhich varies cyclically at 30 cycles per second. Referring to Figure 2,two antennas spaced two j wavelengths apart along the line 0--0 andexcited in phase with each other will produce a radiation patternsubstantially as illustrated,

comprising a broad lobe I7, three approximately evenly spaced narrowlobes I9, 2| and 23, another broad lobe 25 extending opposite the lobeI1, and

three further lobes 21, 29 and 3! similar to and symmetrically disposedwith respect to the lobes 23, 2| and I9 respectively.

Now, using the in-phase condition of Figure 2 as a starting point, letus advance the phase of the excitation of one of the antennas. As thisis done, the lobes I9, 2I and 23 move counterclockwise and the lobes 21,29 and 3| move clockwise. The broad lobe I I gradually splits into twolobes I'! and I1" which move counterclockwise respectively, as indicatedin Figure 3 and Fig-1 ure 4. Figure 3 shows the pattern obtained whenthe phase has advanced 90, and Figure 4 shows the condition.

As the right hand lobe II expands and splits, thelobe 25 contracts anddisappears. Withcon- 'tiiiued advance in phase, the lobes 23 and 21pattern which varies through the fonegoing: second, A radio receivercycle 30- timesper within range of' the transmitter and at some definiteazimuth with respect thereto (say along the dash line 35) will receive asignal. which.

varies cyclically in amplitude. This is caused by the passage ofsuccessive lobesthroughthe-lin-e 35;

Referring to Figures 2, 3 and 4, it isseen that the lobe 23 passesthrough the line 35, and will be followed by the lobes 2|, l9 and; I;T,,and. other subsequent lobes which develop from the right as. the phaseadvances. With a phase rotation, frequency of 30 cycles per second, thefrequency of variationin. signal: amplitude. along: the line 35. (orother radial line from. the midpoint be tween the antennas if. and. 3-);i's:3Q-; oyclespci! SEC? and; It: may be: noted that: this: frequency ofmodulation caused.v by rotation. is not; a function of the antennaspacing.

Beferring'to Figure 6., a. suitable receiver-- and indicator system is;shown. This; is; substantially the; same as that commonly" used; withconven tionalomnidirectional radio: ranges except; for thecalibrations.Azreceivert -l.=,.tuned.inthepIese cnt: ejxamp-e; to; respond to 1:00.kilocyclesr has its. audio output circuit connected; to; two. narrowband passfiiters 3.91 and 4.1-... The filter; ca passes: the onekilocycle subcarrier, with: its 30, cycle modulation, which is;impressed on the-carrier radiated'by thetransm-itter anterma. t.Thefilter 4. I.-

4 lation depends on the bearing of the receiver from the transmitter.Thus, if the line 35 is moved clockwise from its illustrated position,the modulation phase will advance. However, the phase of the 30 cyclemodulation of the 1000 cycle subcarrier is independent of azimuth. Thedifference in phase between the output of the filter H and the; outputof; the rectifier 5,3 is accordingly 2; measure of the angle of thebearing line 35.

Suppose, for example, that the two modulations are in phase when thebearing line 35 coincides withthe, line 35 in Figure 2. Then, as theline 35 moves clockwise, the phase of one modulation passes. the; 30.cycle rotation; frequency module tion produced by the cyclical slippingof radiationl lobes across the line; between transmitter andreceiyer,as. described above.

The. modulated 1.0.00 cycle: output. of the filter 39.is.app1ied:to ademodulator lthwhichldemoduvlates the.- subcarrierto provide. a.constant. phase:

' 3.0. cycle output. This: is. applied to one pair of.

terminals of. av phase; meter 4.5., which m y hoof-f the wattmeter typeor any other known, type, The. 3.0, cycle outputv of the. filter M. is,applied to the other. pair of termi-nalsoi. the. phase. meter. 45..

In addition. to. the phase meter. 45,. a. phase deviation indicator. maybe; provided, compris ing. aphase detector 4.1 oonnectedto the, demodwlater 4.3. and through. an. adjustable. phase. shifter. 49. to. the.filter Al. The. phase. detector 41' may; be. of. the. balanced.rectifier type, which provides. a D..-C.. output whose. magnitude. andpolarity depends on the difference.- in. phase. between. the two.inputs. The output is. applied to. a. zero.- center D..-C... meter 51,.marked L-Rlike. the. visual course indicator. of a conventional radio.range.

The operation of the systemof. Figure. 6. in response. to. signals. of.the. type. transmitted by the system. of Figure 1 has follows I The.receiver and. indicator. system. is. carried. aboard an airplane or.other mobile; craft- .The. hearing from the. transmitter. must. beknown. ap.-- proximately, or determined by auxiliary means such. as a.direction. finder, with an accuracy corresponding to or better than. thewidth. of. one. lobe (say ten degreesl.v Suppose. the mobile crait. to.be. on a line within five. degrees either way from the line 35 ofFigures 2, 3,. 4 and. 5.

-As already described, the received. signal s modulated. in amplitudeowing to. the. rotation of the directive pattern. The. hase of. this.modu x the advances-with respectt'o the other. The advance willbaapproximately, though not necessarily exactly, roportional to theangle a. between the lines. 35.! and. When the line 35 reaches the line35", the phase angle has advanced 360. Further clockwise motion of theline 35 will cause further phase rotation.

It; will? be evident: that the low: frequency: phase reference signalmay be; impressed on. the.

carrier as a. frequency modulation, ratherthan. as; amplitudemodulation. Thiszmay-afford somgre-L duction in crosstalk between the.two low fre.-. quency channels in thereceiyer system. Itisalso feasibleto frequency-modulate the radio ire-e quency carrier with the modulatedsubcarpi'er. With such modulation, the pattern lobes will wobb e. ata1600 cyce rateaboutzmean positions which move at 30- cycl'es as:described. This: will not affect the accuracy of the system, since thedetector will integrate to provide 30: cycle output corresponding to themean positions of the pattern lobes.

Since a change in bearing through an angle-ct 0' degrees will cause achange in phase through anangleof na d'egrees, where nis a constant.de-- pending on the spacing of the transmitter-antem has; theaecuracy ofbearing determination within any sector (such as that between the lines35'" and 35 may be approximatelyn times that which would be obtainedwith the usual single lobedpattern of prior art omnidirectional ranges.This results from the fact that the instrumental errors of the systemare about the same in both cases, while the change in phase in responseto a change in bearing is n times as great in the present-system as inpreviously used systems;

The price of increased accuracy in this caseis loss of uniqueness ofindioation since the phase relations; appearing in the sector betweenthe lines 3 5," and 35- of Figure 2 are, duplicated along correspondingbearin-glines in various'other similar sectors; The scale 45 may be.calibrated in terms of bearing angle, rather than in terms of"phaseangle, In this event, the scale must be replaced. with another whenthe desired course lies in a different, sector. Sectoridentification maybe made by means of a direction finder on themobile. craft, as mentionedabove, or by means of an auxiliary omnidirectional range of thesingle-lobed pattern. type- The, course deviation in ic t r s used. as.n. ordinary radio. range. sy tems to ctandmainr' tam. a prescribedradial. course. to r. rom. the

transmitter. station, The. phase. shifter 59.. is. ads iusted so. hat.the. ou p t. of. the. phase. d tector 41 is zero when the. craf s. onthe. desired course! Deviation from course will cause the outputoi'.the. phase shifter 49, to, advancev or retreat in phase. with. respect.to the. output. of, the rectifier. 6'3... Thephase. detec or. willaccordin ly provid an output whose polarity and. magnitude depends.

5 on the direcuii' fidtntfidiiiit '61 deviation, andthe deviation isindicated on the meter 5|.

The described transmitter system. does not-prO-" vide bearinginformation in all directions. Thus, along the line ---0- in Figures- 2through 5, there is no rotary motion of the pattern lobes, but onlyexpansion and contraction. Complete gangular cgverage through 360degrees, if it is required, may be; obtained by providing anothertransrnitter system like that shown in Figure .l, but withthe antennasinaline at right angles .to fireme For clarity of descriptionandsimplicity of i 1- lustration, it has been assumed that the antennasI and 3 are energized equally, causing the radiation patterns of Figures2 through to go to zero between lobes. In actual practice, this would beundesirable because the percentage modulation of the reference phasesignal would become infinite (i. e. the carrier would disappear) eachtime a pattern null swept through the position line 35. This difficultyis avoided very simply by supplying one antenna, for example the antenna3, with less power than the other. The resulting radiation patterns willbe similar to those shown, except that the minima, will be partialrather than complete.

With the two antenna systems of Figure 1 there is in addition to theabove-described effects, an undesired amplitude modulation at 30 cyclesof the 1000 cycle subcarrier. This may tend to introduce crosstalkbetween the two 30 cycle channels in the receiver-indicator system andcause error unless the detectors 43 and 41 are completely non-responsiveto amplitude variations.

Amplitude modulation of the subcarrier may be prevented by providing athird antenna and an additional single sideband modulator, as shown inFigure 7. As in the system of Figure 1, the antenna l is excited by thecarrier oscillator 5 through the modulator 1, which impresses on thecarrier at 1000 cycle subcarrier frequenc modulated at 30 cycles persecond. Instead of the single antenna 3 of Figure 1, two antennas 53 and51 are provided, one on each side of the antenna l. The antenna 53 isenergized by the 100 kilocycle source 5 through a single sidebandmodulator 59 controlled by the 30 cycle oscillator II, and transmitsonly the lower sideband, whose frequency is 99,970 cycles per second.The antenna 51 is similarly energized through a single sidebandmodulator 6| to transmit only the upper sideband of 100,030 cycles persecond.

The radiation patterns produced bythe system of Figure 7 aresubstantially identical with those shown in Figures 2 through 5,providing the antennas 53 and 5! are each two wavelengths from thecentral antenna I. The signal at the receiver is the same as describedwith reference to the system of Figure 1, except that the 1000 cyclesubcarrier is purely frequency modulated. As in the system of Figure 1,it is preferable to divide the power unevenly between the centralantenna I and the side antennas 53 and 51 to fill in the nulls of theradiation patterns to some extent.

I claim as my invention:

l. A radio range transmitter system, including two omnidirectionalantennas spaced horizontally from each other by a distance d, a Sourceof radio frequency energy of wavelength substantially less than d, meansproviding a composite modulation signal including a constantphase signalof relatively low audio frequency and a signal of substantially higherfrequency r applying the resultant modulated en r y to one 'of saidantennas, and means simultaneously'and: continuously changing the phaseof another portion of said radio frequency energy at a constant rate of360 per cycle of said low audio frequency signal and for applying theresultant phase-shifted radio frequency energy to the other of saidantennas.

2; A radio range system including means generating in space amultiple-lobed radiation pattern which is substantially symmetrical withrespect to a predetermined line and means moving the lobes on one sideof said line clockwise continuously at a constant rate and moving thelobes on the other side of said line counterclockwise continuously atsaid constant rate, and means modulating the radiation in said patternas a whole to provide a distinguishable phase reference signal of afrequency corresponding to the rate of motion of said lobes.

3. A radio range system including two antennas spaced aparthorizontally, a source of radio frequency energy, a modulator connectedbetween the first of said antennas and said source, a second source ofA.-C. energy of a frequency substantially lower than that of said firstsource, a second modulator connected between said source and said firstmodulator, a third source of A.-C. energy of a frequency substantiallylower than that of said second source and means for applying the outputof said third source to said second modulator; a single sidebandmodulator connected between said first source and the second of saidantennas, and means for applying the output of said third source to saidsingle sideband modulator.

4. A radio range system including two horizontally spaced antennas,means exciting one of said antennas with a signal including a radiofrequency carrier, means modulating said carrier by a subcarrier whichis of substantially lower frequency than said carrier and meansmodulating said subcarrier by a constant frequency signal of still lowerfrequency, and single sideband modulating means exciting the other ofsaid antennas with a signal sideband signal of radio frequencydifl'ering in freouency from said carrier by the frequency of saidlowest frequency signal.

5. A radio range system including a central antenna and two sideantennas equally distant from said central antenna and on a lineincluding said central antenna, a source of radio frequency signal ofwavelength substantially less than the spacing between said antennas, asource of low frequency signal, means modulating said radio frequencysignal with said low frequency si nal to provide separately the upperand lower sidebands of said radio frequency signal, means applying saidupper and lower sidebands respectively to said two side antennas, afurther source of Signal of intermediate frequency, means frequencymodulating said last-mentioned signal with said low frequency signal toprovide a com osite modulation signal, means modulating said radiofrequency signal with said composite modulation signal, and meansapplying the resultant signal to said central antenna.

6. A radio range system including a central antenna and two sideantennas, a source of radio frequency signal, a source of low frequencysignal, means modulating said radio frequency signal with said lowfrequency signal to provide sanamtsly -ohe lower sidebamd "01 saidrasiin:frequency sigml, means applying said up= pier and awe: sidgbandsrespeetive'ly 11 sa d WQ side. antennas. a iumzhex m1me off'slg Q1 ofin: immediate ue1;@y. mean n; said, afirmenti ned si n-a l with said.21.9w itrequency si nal to "pr vid a om osite mo ulati n sigma}. meansmedula i g said rad o frequ ncy si n l with salid1comp ite:m du;a;tionSignal, and means app ying the resultant sign l to said central antenna.I

DAVID G. C. LUCK.

r 56? 1mm 13mm:

UNITED m Name 1311: Martin V V May 1, $928 *Campbefl a" me. 11),. "1911pLuck -Aug. 26, 19211 ul er 39311.30, 19;; OBrien Aug. 2-I, I946 BrunnerMagrfZS, T9317 Number 116673792 -1 $138,522 2 ,25 3 i958 2 5 36853 1%2,40 6 ,"BQB 2317.807 '2 5122,1 10

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